Wall papers or Wall Covering have evolved over years. Previously, from a simple paper based material it has moved to high quality Vinyl finish.
The wall Coverings / wall papers come in a roll, you will not get it per sq ft wallpaper piece. The size of this roll is standard i.e 57sq feet which are European and Metric Double rolls and 70 sq ft that are American Double rolls .
In most cases, Wallpapers/wall coverings are generally used as a highlighter on particular wall in a room. This could highlighter behind your TV or behind bed or you decide to use it for one single wall inside room.